The invention relates to a power electronics unit and to a method of producing a power electronics unit, in particular for a device in a motor vehicle, with a sheet-like carrier element, on which interconnects are arranged for the electrical connection of electrical power components and control components of a circuit, likewise located on the carrier element.
In the case of power electronics units of this type, it is known to arrange the interconnects and the power components and control components on an insulating carrier element, which may be a ceramic substrate, a printed circuit board or a DCB substrate. Separate means then have to be used for dissipating the heat generated by the power electronics.
These power electronics units have complex components, need considerable installation space and require great expenditure for their production.
It is therefore an object of the invention to provide a power electronics unit and a method of producing a power electronics unit which is simple and constructed with few components, requires little installation space, permits easy dissipation of the heat generated by the power components and can be produced by a few, simple steps.
This object is achieved according to the invention by the carrier element being a heat sink, on which the interconnects have been applied by means of a heat-conducting adhesive, and a minimum thickness of the heat-conducting adhesive to allow the heat-conducting adhesive to be an electrical insulating layer being ensured by spacers in the heat-conducting adhesive. In this case, the carrier element performs the dual function of substrate and heat sink, it being possible for any low-cost suitable material, including electrically conducting material, to be used for the carrier element, since the heat-conducting adhesive likewise serves with a dual function, not only for heat transmission but also for electrical insulation. To ensure the function of electrical insulation, the heat-conducting adhesive must have a minimum thickness. This is ensured in a way which is simple to produce by the spacers. The arrangement of the heat-producing power components very close to the heat sink and the minimized insulating layer thickness leads to good thermal coupling of the power components to the heat sink and consequently to good and largely direct heat dissipation.
Particularly good heat dissipation is achieved if the heat sink consists of a heat-conducting metal, aluminum or an aluminum alloy being particularly suitable because it is additionally easy to process.
It also leads to a dual function of a component, and consequently to saving of installation space and expenditure on production, if the heat sink is a housing component of a housing accommodating the power electronics.
If the interconnects are produced by punching out or etching out from a copper foil, this requires only little production expenditure.
To be sure to avoid spacers lying on top of one another when producing the power electronics, the spacers may be spherical.
In this case, the spacers preferably consist of an electrically and thermally insulating material, such as glass in particular.
The set object is further achieved by a method of producing a power electronics unit in which a pattern of interconnects is produced from a copper foil by means of punching or etching and is applied by means of a heat-conducting adhesive onto a sheet-like heat sink, in which spacers are mixed in, in which the heat-conducting adhesive is subsequently cured, with the pattern of interconnects being pressed against the heat sink, and in which the power components and control components are thereafter inserted into the pattern of interconnects and soldered.
Only a few, simple production steps are necessary for this method, with the result that the power electronics unit can be produced at low cost. To be able to apply the pattern of interconnects simply onto the heat sink without it being possible for any change to occur in the spatial assignment of the interconnects in relation to one another or possibly also a short-circuit between the interconnects, the copper foil can be covered before the punching or etching with an adhesive tape, which is removed after the pattern of interconnects has been applied onto the heat sink.
In this case, the adhesive tape may be removed before or after the curing of the heat-conducting adhesive.
If appropriate materials are used for the adhesive tape, the removal of the adhesive tape may also be performed by vaporizing during the curing process. It leads to a simple procedure if the heat-conducting adhesive is printed onto the heat sink and the punched-out or etched-out pattern of interconnects is subsequently applied onto the printed-on heat-conducting adhesive.
A further possibility for achieving the object is that, in a method of producing a power electronics unit, a copper foil is applied onto a heat sink by means of a heat-conducting adhesive into which spacers have been mixed, after that the heat-conducting adhesive is cured, with the copper foil being pressed against the heat sink, a pattern of interconnects is subsequently produced from the copper foil by etching and that the power components and control components are subsequently inserted into the pattern of interconnects and soldered. This also allows the handling of an unstable pattern of interconnects to be made easier.
For the curing of the heat-conducting adhesive in the case of the aforementioned methods, heat exposure of the heat-conducting adhesive may additionally take place.
In a way which allows easy handling, the heat-conducting adhesive may be printed onto the heat sink and the copper foil subsequently applied onto the printed-on heat-conducting adhesive. For etching the copper foil, it is coated with a photoresist, exposed after first placing on a mask with a pattern of interconnects cut out in negative form, and subsequently subjected to an etching operation.